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SpringMVC源码阅读:视图解析器

Rest探路者 2019-02-07 11:20:00 阅读数:184 评论数:0 点赞数:0 收藏数:0

1.前言

SpringMVC是目前J2EE平台的主流Web框架,不熟悉的园友可以看SpringMVC源码阅读入门,它交代了SpringMVC的基础知识和源码阅读的技巧

本文将通过源码(基于Spring4.3.7)分析,弄清楚SpringMVC如何完成视图解析的

2.源码分析

SpringMVC源码阅读:拦截器分析过doDispatch的运行过程,这里再分析一遍

回到DispatcherServlet类的doDispatch方法,看看doDispatch如何获取ModelAndView

HandlerMapping根据request获得HandlerExecutionChain

根据HandlerExecutionChain获取HandlerAdapter

HandlerAdapter根据request,response和HandlerExecutionChain调用handle方法返回ModelAndView

然后交由processDispatchResult处理

1023行检测从doDispatch方法运行到此是否有异常

1037行根据ModelAndView渲染视图

1259根据视图名称解析成View对象

1282行调用AbstractView的render方法进行渲染

点进去,这里以解析ftl做测试

301行创建包含动态值和静态属性的Map

302为待渲染的响应做准备

303行调用子类实现方法渲染这个包含动态值和静态属性的Map

接下来会进入AbstractTemplateView的renderMergedOutputModel方法,AbstractTemplateView是AbstractView的子类

AbstractTemplateView的renderMergedOutputModel方法会调用内部renderMergedTemplateModel方法,该方法被子类FreemarkerView实现

打开FreemarkerView的renderMergedTemplateModel方法

进入doRender方法,该方法根据response渲染FreeMarker视图

275行exposeModelAsRequestAttributes方法在父类AbstractView被实现,该方法把Model设置到request中

277行创建Freemarker模板模型

284行处理、加工Freemarker模板给response

 

再看看FreeMarkerViewResolver做了什么,打开类接口继承图

构造函数设置了前缀和后缀,再看看AbstractTemplateViewResolver

104~108行给视图设置属性

我们发现103行super引用了父类,点开进入UrlBasedViewResolver的buildView方法

532行拼接前缀+视图名称+后缀,例如"employee/form.ftl",并设置url

534~553行判断属性是否为空,非空则设置到View中

再看createView方法

460行如果以"redirect:"开头,交给RedirectView处理

467行如果以"forward:"开头,交给InternalResourceView处理

Freemarker解析逻辑至此分析完毕

 

现在看JSP的解析流程

回到AbstractView类的render方法,刚刚我们分析过

304行此时renderMergedOutputModel方法被子类InternalResourceView实现

 

139行将Model设置到Request中

142将辅助性参数设置到Request中

145行获取视图文件路径

148行获取请求分发器

155到170行如果response已经提交,则把资源文件纳入到response中,否则调用forward方法转发

再看下InternalResourceViewResolver,该类辅助InternalResourceView,为其设置属性,其余的ViewResolver的实现类分析同Freemarker

3.自定义视图解析

3.1 自定义支持Freemarker和Jsp的视图解析器

自定义视图解析器,"jsp:"开头构造InternalResourceView解析jsp,以"freemarker:"开头则构造FreemarkerView解析ftl

这样做的好处是可以区分同名的jsp和ftl

public class CustomViewResolver extends UrlBasedViewResolver {
public static final String JSP_URL_PREFIX = "jsp:";
public static final String FTL_URL_PREFIX = "freemarker:";
private static final boolean jstlPresent = ClassUtils.isPresent(
"javax.servlet.jsp.jstl.core.Config", CustomViewResolver.class.getClassLoader());
private Boolean exposePathVariables = false;
private boolean exposeRequestAttributes = false;
private boolean allowRequestOverride = false;
private boolean exposeSessionAttributes = false;
private boolean allowSessionOverride = false;
private boolean exposeSpringMacroHelpers = true;
public CustomViewResolver() {
this.setViewClass(FreeMarkerView.class);
}
@Override
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
if(viewName.startsWith(FTL_URL_PREFIX)) {
return buildFreemarkerView(viewName.substring(FTL_URL_PREFIX.length()));
} else if(viewName.startsWith(JSP_URL_PREFIX)) {
Class viewCls = jstlPresent ? JstlView.class : InternalResourceView.class;
return build(viewCls, viewName.substring(JSP_URL_PREFIX.length()), getPrefix(), ".jsp");
} else {
//默认以freemarker处理
return buildFreemarkerView(viewName);
}
}
/**
* @Author 谷天乐
* @Description 使用UrlBasedViewResolver的buildView方法
* 因为CustomViewResolver重写了buildView,不再执行UrlBasedViewResolver的buildView方法
* @Date 2019/1/17 11:26
* @Param [viewClass, viewName, prefix, suffix]
* @return org.springframework.web.servlet.view.AbstractUrlBasedView
**/
private AbstractUrlBasedView build(Class viewClass, String viewName, String prefix, String suffix) {
AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
view.setUrl(prefix + viewName + suffix);
String contentType = getContentType();
if (contentType != null) {
view.setContentType(contentType);
}
view.setRequestContextAttribute(getRequestContextAttribute());
view.setAttributesMap(getAttributesMap());
if (this.exposePathVariables != null) {
view.setExposePathVariables(exposePathVariables);
}
return view;
}
/**
* @Author 谷天乐
* @Description 使用AbstractTemplateViewResolver的buildView,为view设置属性
* Freemarker解析所需
*
* @Date 2019/2/7 10:22
* @Param [viewName]
* @return org.springframework.web.servlet.view.AbstractUrlBasedView
**/
private AbstractUrlBasedView buildFreemarkerView(String viewName) throws Exception {
AbstractTemplateView view = (AbstractTemplateView) build(FreeMarkerView.class, viewName, "", getSuffix());
view.setExposeRequestAttributes(this.exposeRequestAttributes);
view.setAllowRequestOverride(this.allowRequestOverride);
view.setExposeSessionAttributes(this.exposeSessionAttributes);
view.setAllowSessionOverride(this.allowSessionOverride);
view.setExposeSpringMacroHelpers(this.exposeSpringMacroHelpers);
return view;
}
public boolean isExposeRequestAttributes() {
return exposeRequestAttributes;
}
public void setExposeRequestAttributes(boolean exposeRequestAttributes) {
this.exposeRequestAttributes = exposeRequestAttributes;
}
public boolean isExposeSessionAttributes() {
return exposeSessionAttributes;
}
public void setExposeSessionAttributes(boolean exposeSessionAttributes) {
this.exposeSessionAttributes = exposeSessionAttributes;
}
public boolean isExposeSpringMacroHelpers() {
return exposeSpringMacroHelpers;
}
public void setExposeSpringMacroHelpers(boolean exposeSpringMacroHelpers) {
this.exposeSpringMacroHelpers = exposeSpringMacroHelpers;
}
}

在dispatcher-servlet.xml加入自定义视图解析器

 <bean class="org.format.demo.custom.CustomViewResolver">
<property name="prefix" value="/WEB-INF/view/"/>
<property name="suffix" value=".ftl"/>
<property name="contentType" value="text/html;charset=utf-8"/>
<property name="exposeRequestAttributes" value="true"/>
<property name="exposeSessionAttributes" value="true"/>
<property name="exposeSpringMacroHelpers" value="true"/>
<property name="requestContextAttribute" value="request"/>
</bean>

引入freemarker和jsp的配置,配置在前遇到同名情况具备更高的优先级,比如index.ftl和index.jsp会优先解析index.ftl

 <!--遇到同名的ftl和jsp文件,配置在前的解析器优先级更高-->
<import resource="classpath:springConfig/viewConfig/freemarker.xml"/>
<import resource="classpath:springConfig/viewConfig/jsp.xml"/>

测试Controller

@Controller
@RequestMapping(value = "/tvrc")
public class TestViewResolverController {
@RequestMapping("jsp")
public ModelAndView jsp(ModelAndView view) {
view.setViewName("jsp:tvrc/test");
return view;
}
@RequestMapping("/ftl")
public ModelAndView freemarker(ModelAndView view) {
view.setViewName("freemarker:tvrc/test");
return view;
}
}

浏览器输入http://localhost:8080/springmvcdemo/tvrc/jsp

 

浏览器输入http://localhost:8080/springmvcdemo/tvrc/ftl

 

3.2 自定义Pdf视图

测试Controller

@Controller
@RequestMapping("otherview")
public class OtherViewController {
@RequestMapping("/pdf")
public ModelAndView mypdf() {
ModelAndView mav = new ModelAndView();
//添加自定义视图
mav.setView(new MyPdfView());
List<String> list = new ArrayList<String>();
for (int i = 0; i < 10; i++) {
list.add(i+"");
}
mav.addObject("list", list);
return mav;
}
@RequestMapping("/excel")
public ModelAndView myexcle() {
ModelAndView mav = new ModelAndView();
//添加视图
mav.setView(new MyExcelView());
List list = new ArrayList<String>();
for (int i = 0; i < 10; i++) {
list.add(i+"");
}
mav.addObject("list", list);
return mav;
}
}

创建测试类继承AbstractPdfView,重写buildPdfDocument方法

public class MyPdfView extends AbstractPdfView {
@Override
protected void buildPdfDocument(Map<String, Object> model, Document document, PdfWriter writer,
HttpServletRequest request, HttpServletResponse response) throws Exception {
List list = (List) model.get("list");
for (int i = 0; i < list.size(); i++) {
//将数据加载到视图上
document.add(new Paragraph((String)(list.get(i))));
}
}
}

浏览器输入http://localhost:8080/springmvcdemo/otherview/pdf

3.3 自定义Excel视图

创建测试类继承AbstractExcelView,重写buildExcelDocument方法

public class MyExcelView extends AbstractExcelView {
@Override
protected void buildExcelDocument(Map<String, Object> model, HSSFWorkbook workbook, HttpServletRequest request,
HttpServletResponse response) throws Exception {
HSSFSheet sheet;//工作簿的名字
HSSFCell cell;//单元格

sheet = workbook.createSheet("spring");
sheet.setDefaultColumnWidth(12);
List list = (List) model.get("list");
for (int i = 0; i < list.size(); i++) {
cell = getCell(sheet, 0, i);
setText(cell, (String) list.get(i));
}
}
}

 浏览器输入http://localhost:8080/springmvcdemo/otherview/excel

4.总结

View作为视图接口,AbstractView的render方法创建待渲染的model,调用子类,如果待解析视图类型是jsp,则调用InternalResourceView,如果是ftl,则调用FreemarkerView,执行渲染

ViewResolver作为视图解析接口,主要为View提供支持,createView方法创建View,buildView根据路径构造View,并为View设置一系列属性

DispatcherServlet根据ModelAndView调用View实现类的render方法进行视图渲染,ViewResolver实现类起到辅助作用,为View设置属性(前缀、后缀等)

5.参考

https://docs.spring.io/spring/docs/4.3.7.RELEASE/spring-framework-reference/htmlsingle/#beans-beans-conversion

https://docs.spring.io/spring/docs/current/javadoc-api/

https://github.com/spring-projects/spring-framework

文中难免有不足,欢迎指出

版权声明
本文为[Rest探路者]所创,转载请带上原文链接,感谢
https://www.cnblogs.com/Java-Starter/p/10353996.html

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